The present invention relates to improvements in closure devices for plastic storage bags, and more particularly, to an end stop for use on a plastic reclosable fastener and a method of installation thereon.
The use of closure devices for fastening storage containers, including plastic bags, is generally known. Furthermore, the manufacture of closure devices made of plastic materials is generally known to those skilled the in the art, as demonstrated by the numerous patents in this area.
A particularly well-known use for closure devices is in connection with flexible storage containers, such as plastic bags. In some instances, the closure device and the associated container are formed from thermoplastic materials, and the closure device and the sidewalls of the container are integrally formed by extrusion as a single piece.
Alternatively, the closure device and sidewall of the container may be formed as separate pieces and then connected by heat sealing or any other suitable connecting process. In either event, such closure devices are particularly useful in providing closure means for retaining matter within the bag.
Conventional closure devices typically utilize mating fastening strips or closure elements, which are used to selectively seal the bag. In addition, sliders may be provided for use in opening and closing the fastening strips. Such reclosable bags equipped with sliders are known in the art as xe2x80x9cslider bags.xe2x80x9d The slider may include a separator which extends at least partially between the fastening strips. When the slider is moved in the opening direction, the separator divides or deoccludes the fastening strips and opens the bag. When the slider is moved in the closing direction, the slider closes or occludes the fastening strips.
It is well known in the art to provide one or both ends of the reclosable fastener of a slider bag with an end stop to prevent movement of the slider past the ends of the bag. The end stop may be formed from the material of the fastening strips such that they protrude transversely from the fastener a distance adequate to engage the slider and prevent movement of the slider passed the respective ends of the bag as is known from U.S. Pat. No. 5,950,285 to Porchia et al. With this arrangement the size of the end stops is limited by the amount of material in the ends of the fastener.
Another prior art end stop arrangement is disclosed in U.S. Pat. No. 5,161,286 to Herrington et al. In this patent the end stops are located at the opposite ends of the reclosable fastener and each end stops is fashioned as a pair of clamp members connected together by a flexible strap which extends over the top of the zipper and which are also secured together by a plastic rivet that pierces the film material of the bag below the reclosable fastener. A drawback with this approach is the potential for leakage that may occur anytime the bag is pierced.
U.S. Pat. No. 5,448,807 to Herrington discloses another prior art end stop arrangement in which the end stop is formed as a separate plastic clip that is fused with the ends of the fastening strips of a zipper type reclosable fastener during manufacture of the bag. In accordance with the manufacturing method aspect of the invention, this patent document teaches to position the clip at opposite ends of the reclosable fastener, the clip comprising a strap member that is wrapped over the top of the zipper, and then sealing in place along with the profile elements of the fastening strips to form a fused mass. This patent document further teaches to use an insertion device to hold the clips in place while they are being sealed to the zipper. In order to hold the clips in place by themselves, the clips may be provided with an integral pin that penetrates the zipper film. Thus, in the line production of thermoplastic bags, the multiple steps of positioning the end stop on the bag, holding the end stop in place prior to fusing, and fusing the end stop to the bag are done in a lengthy sequence at a single station on the line. The lengthy sequence of steps at a single station in a line production results in slow line speed and low throughput.
It would be desirable to position and secure end stops on a reclosable fastener of a thermoplastic bag in the line production of thermoplastic bags in a manner in which increased line speed and greater throughput are achieved.
The present invention is directed to an end stop for a thermoplastic bag having a reclosable fastener at the open top end of the bag. The reclosable fastener comprises a pair of interlocking fastening strips. The end stop is configured to facilitate snap fit insertion onto the fastener strips and includes a top portion and a pair of depending side portions that straddle the fastener. The side portions further include inwardly directed tab and shoulder structure that engage the reclosable fastener and prevent the end stop from being inadvertently pulled off in a transverse direction in order to hold the end stop in place prior to being bonded to the bag. The bonding step is preferably accomplished by ultrasonic welding.
In the case of the line production of thermoplastic bags wherein a continuous web of plastic material is moved from one station to the next, the invention allows for the positioning of the end stop onto the reclosable fastener at a first station and the bonding of the end stop to the bag at a second station. The positioning and bonding steps may be performed simultaneously since the tab and shoulder structure hold the end stop in place on the reclosable fastener as the web of plastic material is moved from the first station to the second station. The ability to perform the simultaneous sequence of steps described above advantageously provides for increased line speed production and throughput.
The bags may include a slider for use in opening and closing the reclosable fastener. The slider is slidably disposed on the interlocking fastening strips for facilitating the occlusion and deocclusion of the fastening strips when moved towards first and second ends of the fastening strips. The first and second ends of the fastening strips are secured together and the end stop is provided to the first, closing end of the fastening strips. The end stop may be provided with quick release latching structure engagable with cooperating latch-receiving structure provided to the mating or opening end of the slider to secure the slider when it is moved into engagement with the end stop at the closing end of the bag. In accordance with an alternate embodiment, a second end stop may be provided at the other end of the bag.
Methods and apparatus which incorporate the features described above and which are effective to function as described above constitute further, specific objects of the invention. Other objects and advantages of the invention will become apparent upon reading the following description and upon reference to the drawings.